1. Field of the Invention
The present invention relates to a method of producing soyasapogenol B using a microbial culture, and to a novel strain which belongs to genus Neocosmospora and a novel strain which belongs to genus Eupenicillium. 
2. Background Art
Soyasapogenol B is one of the aglycones of saponins contained in legumes and was first isolated from soybean seeds (Glycine max MERRILL, seeds) and its structure has been determined (Chem. Pharm. Bull. 24: 121-129, 1976, Chem. Pharm. Bull. 30: 2294-2297, 1982). Glycosides (e.g., soyasaponin) having soyasapogenol B as an aglycone have been reported to have various physiological activities, such as antioxidation effect, hepatoprotective effect, serum lipid improving effect, platelet aggregation suppressing effect, and anticomplementary activity, and their potential use as preventive and therapeutic drugs for immune diseases, such as nephritis, rheumatism and systemic lupus erythematosus, autoimmune diseases, and thrombosis is indicated (Kagaku to Seibutsu 21:224-232, 1983; Japanese Patent Laid-open Publication No.37749/1986). Further, as for soyasapogenol B, anticomplementary activity, platelet aggregation suppressing effect, and growth suppressing effect on cells derived from human colon cancer and human ovarian cancer have been reported (Japanese Patent Laid-open Publication No.37749/1986; Japanese Patent Laid-open Publication No.234396/1998).
Soyasapogenol B can be obtained, for example, by chemically hydrolyzing sugar chains of soyasaponins I-V contained in soybean seeds. However, this is not an effective production method because a considerable number of by-products are produced under the conditions for acid hydrolysis or the like. Furthermore, when a crude extract derived from soybeans is used as the material for the chemical hydrolysis, aglycones other than soyasapogenol B are produced at the same time because this crude extract contains soyasaponins A1-A6 or the like, other than soyasaponins I-V, which complicates the purification process and causes other problems.
On the other hand, as for methods of producing soyasapogenol B using microorganisms, a method with genus Streptomyces (Chem. Pharm. Bull. 32: 1287-1293, 1984) and a method with genus Penicillium (Japanese Patent Laid-open Publication No. 234396/1998) are known. However, these methods of producing soyasapogenol B are not sufficient for productivity and practicality. Further, it has been reported that soyasapogenol B is produced as a by-product when an acidic oligosaccharide having glucuronic acid as the reducing end terminal is produced upon hydrolyzing a glucuronide saponinusing the enzyme (glucuronidase) produced by microorganisms that belong to genus Aspergillus or a culture containing this enzyme (Japanese Patent Publication No. 32714/1995). However, this method is primarily a method of producing acidic oligosuccharides, and only a qualitative confirmation of soyasapogenol B is described.
As mentioned above, soyasapogenol B has various physiological activities wherein its use as a pharmaceutical or health food, or as a material for derivatives of further improved usefulness can be expected. Accordingly, there are needs to develop more efficient and less costly methods of producing soyasapogenol B.